Lithium Migration in Li₄Ti₅O₁₂ Studied Using in Situ Neutron Powder Diffraction

Abstract

We used in situ neutron powder diffraction (NPD) to study the migration of Li in Li4Ti5O12 anodes with different particle sizes during battery cycling. The motivation of this work was to uncover the mechanism of the increased capacity of the battery made with a smaller-particle-sized anode. In real time, we monitored the anode lattice parameter, Li distribution, and oxidation state of the Ti atom, and these suggested an increase in the rate of Li incorporation into the anode rather than a change in the migration pathway as a result of the particle size reduction. The lattice of these anodes during continuous lithiation undergoes expansion followed by a gradual contraction and then expansion again. The measured lattice parameter changes were reconciled with Li occupation at specific sites within the Li4Ti5O12 crystal structure, where Li migrates from the 8a to 16c sites. Despite these similar Li-diffusion pathways, in larger-particle-sized Li4Ti5O12 the population of Li at the 16c site is accompanied by Li depopulation from the 8a site, which is in contrast to the smaller-particlesized anode where our results suggest that Li at the 8a site is replenished faster than the rate of transfer of Li to the 16c site. Fourier-difference nuclear density maps of both anodes suggest that 32e sites are involved in the diffusion pathway of Li. NPD is again shown to be an excellent tool for the study of electrode materials for Liion batteries, particularly when it is used to probe real-time crystallographic changes of the materials in an operating battery during charge-discharge cycling. KEYWORDS: in-situ neutron diffraction, lithium ion battery, lithium titanium oxide, particle size, lithiation and delithiation mechanism.ABSTRACT: We use in-situ neutron powder diffraction (NPD) to study the migration of Li in Li 4 Ti 5 O 12 anodes with different particle sizes during battery cycling. The motivation of this work was to uncover the mechanism for increased capacity of the battery made with a smaller particle-sized anode. We monitor in real time the anode lattice parameter, Li distribution, and the oxidation state of the Ti atom, with these suggesting an increase in the rate of Li incorporation into the anode rather than a change in migration pathway as a result of the particle size reduction. The lattice of these anodes during continuous lithiation undergoes expansion, followed by a gradual contraction, and lastly expansion again. The measured lattice parameter changes are reconciled with Li occupation at specific sites within the Li 4 Ti 5 O 12 crystal structure, where Li migrates from the 8a to 16c sites. Despite these similar Li diffusion pathways, in the larger particle-sized Li 4 Ti 5 O 12 the population of Li at the 16c site is accompanied by Li depopulation from the 8a site, in contrast to the smaller particle-sized anode where our results suggest that the Li at the 8a site is replenished faster that the rate of transfer of Li to the 16c site. Fourier-difference nuclear density maps of both anodes suggest that 32...

Electrochemistry and structure of the cobalt-free Li1+xMO2(M = Li, Ni, Mn, Fe) composite cathode

“…The use of deuterated electrolyte with a heavier molecular-mass and higher viscosity can be detrimental to battery performance, as noted in previous work. [42][43][44][45][46] The incremental capacity-plot (Figure 4) exhibits features only from the couples expected to be redox-active between 3 and 4.3 V, which correspond to Ni 2+ /Ni 3+ and Ni 3+ /Ni 4+ transitions, respectively. 47 The absence of a peak around 3 V indicates the Mn 3+ /Mn 4+ redox couple is inactive and that no or minor amounts of Mn 3+ are present in the cathode.…”

Structure of the Li4Ti5O12 anode during charge-discharge cycling

“…The two-phase reaction between LiFePO 4 and FePO 4 in cathode is also observed in Figure 3. To effectively refine the O positional parameter, it was necessary to fix the Li occupancy at 8a and 16c sites in the sequential Rietveld refinement, as per previous work (Pang et al, 2014a;Pang et al, 2014b). During charge, the anode lithiates and the lattice undergoes rapid expansion, followed by a gradual contraction.…”

In situ methods for Li-ion battery research: A review of recent developments

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